1The following are demonstrations of the rfsio.d script.
2
3
4
5Here we trace file read() activity that has fully missed the cache and 
6must be read from disk,
7
8   # ./rfsio.d
9   
10   Read IOPS (count)
11   /                                   logical          7
12   /extra1                            physical        162
13   /boot                               logical        235
14   /boot                              physical        410
15   /extra1                             logical       9514
16   
17   Read Bandwidth (bytes)
18   /                                   logical        533
19   /boot                               logical    1502386
20   /boot                              physical    1512960
21   /extra1                            physical   97153024
22   /extra1                             logical   97228668
23   
24   Total File System miss-rate: 100%
25   ^C
26
27The miss rate of 100% means that all of the file system activity missed
28the cache, and had to read from disk.
29
30
31
32The following demonstrates file read() activity to the root filesystem
33that mostly returned from the file system cache.
34
35   # ./rfsio.d
36   
37   Read IOPS (count)
38   /                                  physical          1
39   /extra1                            physical          9
40   /devices                            logical          9
41   /                                   logical         15
42   /extra1                             logical       4096
43   
44   Read Bandwidth (bytes)
45   /devices                            logical          9
46   /                                   logical        949
47   /                                  physical       8192
48   /extra1                            physical     917504
49   /extra1                             logical    4194304
50   
51   Total File System miss-rate: 22%
52   ^C
53
54The total miss-rate was 22%, which is based on the bytes transferred that
55missed the cache.
56
57
58
59
60Now for an unusual demonstration,
61
62   # ./rfsio.d
63   
64   Read IOPS (count)
65   /devices                            logical          1
66   /                                   logical         10
67   /extra1                            physical        106
68   /extra1                             logical       6337
69   
70   Read Bandwidth (bytes)
71   /devices                            logical          2
72   /                                   logical        961
73   /extra1                             logical   64846450
74   /extra1                            physical   66151424
75   
76   Total File System miss-rate: 102%
77   ^C
78
79Here the miss-rate is 102%, which indicates that more data was read from 
80disk than was requested; this can occur due to UFS read-ahead, which
81assists the performance of sequential disk activity at the small risk of
82reading too much data.  
83